When Boulder Philharmonic Orchestra music director Michael Butterman announced the all-Mozart concert that would be the second classical subscription event of the current season, he almost invited skepticism. Attempting to emulate, at least in some ways, the concert practices of the 18th century seemed to be at best a gimmick and at worst an indulgence.The skepticism proved unfounded Saturday night at Macky Auditorium. The concert was an extremely enjoyable evening that brought memories of the long-departed Sinfonia of Colorado, which specialized in Mozart's works. It was one of Butterman's most effective programs yet, and the orchestra was in excellent form.Sure, it was a strange idea to play the first movement of a symphony (the "Haffner" ) at the beginning of the concert as a quasi-overture, leaving the other three movements for the end, but it was something Mozart did. And it worked wonderfully. There is much to be said for 20th-century concert conventions, where the musical work is an unalterable, inseparable entity, but opening the mind to the practices of the past shows that they were by no means misguided. The symphony as bookend helped to unify the entire evening.At center stage were the three guest artists. Violinist Brian Lewis brought enthusiasm and joy to his performance of the last violin concerto, the so-called "Turkish." Particularly effective were his choices of well-constructed cadenzas by Franz Beyer and Joseph Joachim, supplemented by his own additions. Lewis' slow second movement was especially beautiful. The orchestral cellos and basses made the most of their "Turkish" effects in the last movement.Soprano Bonnie Draina and mezzo-soprano Adriana Zabala presented arias and a duet from various Mozart operas over the course of the evening. Zabala had the most-familiar pieces, Cherubino's arias from "Le Nozze di Figaro" and Zerlina's song from "Don Giovanni."But Draina, fondly remembered for some superl